For all types of substrates, perpendicular magnetic recording (PMR) technology is being employed in an effort to increase areal density. Generally, PMR media may be partitioned into two primary functional and structural regions: a soft magnetic underlayer (SUL) and a magnetic recording layer(s) (RL). FIG. 1 illustrates portions of a conventional perpendicular magnetic recording disk drive system having a recording head 101 including a trailing write pole 102 and a leading return (opposing) pole 103 magnetically coupled to the write pole 102. An electrically conductive magnetizing coil 104 surrounds the yoke of the write pole 102. The bottom of the opposing pole 103 has a surface area greatly exceeding the surface area of the tip of the write pole 102. As the magnetic recording disk 105 is rotated past the recording head 101, current is passed through the coil 104 to create magnetic flux within the write pole 102. The magnetic flux passes from the write pole 102, through the disk 105, and across to the opposing pole 103 to record in the PMR layer 150. The SUL 110 enables the magnetic flux from the trailing write pole 102 to return to the leading opposing pole 103 with low impedance.
Typically, higher areal densities are achieved with well-isolated smaller grains in the PMR layer. A higher magnetocrystalline anisotropy constant (Ku) is typically required to resist the demagnetization effects of the perpendicular geometry and to keep the smaller grains thermally stable to reduce media noise. For example, smaller grain size (<7 nm) and high magnetocrystalline anisotropy (Ku) L10 ordered FePt media can achieve areal density beyond 1 Tb/in2 magnetic recording.
High density perpendicular magnetic recording (PMR) medium requires high signal to noise ratio (SNR) and high thermal stability (high KuV/kT). Small grains with high grain density and good crystallographic orientation of the c-axis perpendicular to the plain of the media, i.e., narrow c-axis dispersion, can reduce medium noise and increase SNR. For PMR media the grain size can be reduced by decreasing the thickness of the IL that the magnetic layer is deposited on, or by using high deposition pressure. However, c-axis dispersion can be degraded by decreasing the IL thickness or using too high deposition pressure.
Increasing the thickness of the IL Ru in current PMR media can reduce the Δθ50 of the Ru (00.2) and Co (00.2). However, there is a trade off between Δθ50 and grain size. Thicker IL increases grain size and also increases the spacing from the SUL, thereby reducing the media writability. It would be beneficial to reduce IL thickness to improve OW under narrow track pitch recording.
Using high IL deposition pressure can also reduce grain size. However, this may introduce undesirably many voids and defects and therefore harm reliability performance.